A number of inventions have been directed to the recovery of hydrocarbons from an underground reservoir or formation.
Canadian Patent No. 1,130,201 (Butler) teaches a thermal method for recovering normally immobile oil from an oil sand deposit utilizing two wells, one for injection of heated fluid and one for production of liquids. Thermal communication is established between the wells and oil drains continuously by gravity to the production well where it is recovered.
U.S. Pat. No. 6,257,334 (Cyr. et al.) teaches a thermal process for recovery of viscous oil from a subterranean reservoir involving the use of an offset well. A pair of vertically spaced, parallel, co-extensive, horizontal injection and production wells and a laterally spaced, horizontal offset well are provided. The injection and production wells are operated as a Steam-Assisted Gravity Drainage (SAGD) pair. Cyclic steam stimulation is practiced at the offset well. The steam chamber developed at the offset well tends to grow toward the steam chamber of the SAGD pair, thereby developing communication between the SAGD pair and the offset well. The offset well is then converted to producing heated oil and steam condensate under steam trap control as steam continues to be injected through the injection well.
U.S. Pat. No. 7,556,099 (Arthur et al) describes a thermal process for recovery of viscous oil from a subterranean reservoir whereby an infill well is provided in a bypassed region between adjacent well pairs, the bypassed region formed when respective mobilized zones of the adjacent well pairs merge to form a common mobilized zone. In a preferred embodiment, injection and production well pairs are operated as a Steam-assisted Gravity Drainage (SAGD) pair. The infill well is operated to establish fluid communication between the infill well and the common mobilized zone. Once such fluid communication is established, the infill well and the adjacent well pairs form a single hydraulic and thermal unit operating under a gravity-dominated recovery process.
U.S. Pat. No. 4,727,937 (Shum et al) describes a steam based process for recovery of hydrocarbons which employs a plurality of infill wells. Four horizontal producer wells are drilled along the sides of a rectangle. A vertical steam injection well is then placed in the center of the well pattern, and four vertical infill wells are located midway between the central injection well and the four corners of the rectangular well pattern. Steam is initially injected through the central injection well and production is taken at the four infill wells. After the injection of about 0.5 to about 1.0 pore volumes of steam through the central injection well, the central injector is converted to water, the infill production wells are converted to steam injection, and production is taken from the horizontal wells. This patent differs from both the prior art cited above as well as from the present invention in several material aspects, including the roles and functions of the infill wells. However, most notably, this patent involves horizontal displacement of hydrocarbon by steam and does not employ gravity drainage or a gravity-dominated recovery process.
U.S. Pat. No. 4,637,461 (Hight) describes a 9-spot pattern involving vertical wells at the center, corners, and mid-point of the sides of the pattern, as well as eight horizontal wells, each horizontal well drilled between a corner and a side vertical well. In addition, vertical infill wells are located mid-way between the central injector and the corner wells. The recovery process described in the patent involves horizontal displacement. The option to complete the wells lower in the formation to recognize the tendency of steam to rise within the formation is also described. However, this is still totally within the context of a recovery process which relies on horizontal displacement. As such, this patent does not employ, or largely rely on, gravity drainage or a gravity-dominated recovery mechanism.
U.S. Pat. No. 4,620,594 (Hall) describes a set of techniques aimed at recovering additional oil after steam override between an injector and a producer in a steam displacement process (i.e., steam drive) has resulted in a condition whereby continued operation of the injector-producer well pair will not provide an economic means of recovering the bypassed oil. The techniques described for recovering the bypassed oil include re-perforating the two wells and reversing their roles, introducing a fluid to block or impede flow in the high mobility override zone and introducing a single infill well. However, all of these techniques, including specifically the use of a single infill well, are described within the context of a displacement process, with no reference to a gravity drainage mechanism or gravity-dominated recovery process.
U.S. Pat. No. 4,166,501 (Korstad et al), describes a steam displacement (i.e., steam drive) oil recovery process employing an injection well and a production well with an infill well being located in the recovery zone between the injection well and production well. Steam is injected into the injection well and oil recovered from the production well until steam breakthrough occurs at the production well, after which the infill well is converted from a producer well to an injector well, and steam is injected into the infill well with production being continued from the production well. Application of Korstad et al results in a “significant increase in the vertical conformance of the steam drive oil recovery process”. U.S. Pat. Nos. 4,166,502; 4,166,503; 4,166,504; and 4,177,752 describe variations in the steam drive enhanced oil recovery process employing infill wells described in U.S. Pat. No. 4,166,501 above. In all cases, the basic recovery process is steam displacement, and there is no reference to employing a gravity drainage mechanism or a gravity-dominated recovery process.
It is, therefore, desirable to provide an improved gravity-dominated recovery process employing multiple infill wells.